I am not an Expert on them 351m's and 400m's . But I have done some work on them . I had a 351m in a 1977 F250 4X4 that I owned . And My Father had a 1974 LTD with a 400m . That 400m has good torque . Basically the M's are Like 351 Cleveland's with a .0050 inch taller deck and use the 385-429/460 Bell-housing bolt pattern .

Both the 351m and 400m used open chamber 2V port heads . I don't think Ford ever made a M with a Factory 4bbl . But Edelbrock make 4bbl intake for the taller M blocks .

The Best heads to use on that 400m are Mid 70's 351 Cleveland 2V 74.7 to 77.7 open chamber heads . They will breath much better and make 9.5.1 C/R with stock M pistons .

I will have to look into it a little more than the Vin says 351m so maybe someone changed out the dash or swapped motors long ago. The block that came out was beyond repair so now I have all the parts off it. Just hate to see a pair of Cleveland heads collecting dust. If I can't do this I will find another block and build it.

Hey tango I just read the article you posted about installing a 400m into a 351 stroker. I did a little more searching on my current Cleveland parts and it seems they are off a 74 Cleveland 4v open chamber heads. In these later years of the 4v heads they had the 2v valves with 4v ports. Is there anywhere that makes the intake spacer for swapping the 400 heads and intake or will I have to find a place to Fab that. I would like to do this swap it looks like in the article they got some decent gains with these parts and a 0.030 over bore.

So if I have it right you want to Bolt on some Mid 70's 351C 4V Heads to a 400M Block . I have to do some Looking up to see if a Manifold is Made to do that swap . If not Like you said someone most Likely make spacers to adapt a 351C intake to an M Block .

I took a look at those links and the first one seems more achievable. But he was missing one small bit of info the 74 Cleveland heads I have and maybe 73 have the 4v ports and the smaller 2v valves as a emissions measure. But on that first build he is saying the 2v beds were better because of the valves they would produce more low end torque.

I think the heads I have would be perfect for What I'm trying to do better flow more torque and just by putting them on the CR goes up to about 8.86 should be able to get 9 or more with the milling I have to do to the heads. The only problem is the 4v heads will not match up well with the 400 stock intake. And with deck height difference the 4v Cleveland intake comes up a little short on each side and I have seen and heard that spacers can be made to make up the difference.

I would love to do this mod and have to do some measuring and a lot of thinking to make sure it is done right. It will be a project but it will be unique fun and pay off when done. I will post pics of this if it works out.

In the one article they talk about the intake Spacers that should not be a Problem then you will use a 351C 4V intake . The Problem on any Engine with a Non-Adjustable Valve Train is . The Valve Pre Load is set with the stock Deck and Gasket thickness type . So when You mill heads or run thinner Gaskets you add more Pre-Load on the Lifters a Little bit may be ok . But to much and you will need adjustable Push rods and or adjustable Rockers .

At first I am just going to try the head and intake swap with the regular gasket and 0.010 milled just for cleanup purposes. I think that should keep it safe for now. I will look up the pre load numbers for both motors and the strength of springs and rocker arm ratios to see just how close all the numbers are. Just by looking at them it is hard to tell them apart aside from port size. And if this swap works out well or with little changing of internals needed I may just call that good if I start having to do lifters and rocker arms and springs and such I will get a fully compatible kit with a cam. More work but I think the outcome would be a truck that could tow just about whatever I wanted I was impressed with the torque numbers even with a somewhat simple build.

The problem I have with this truck is the original owner spent the money on all heavy duty running gear and axles and suspension and it works great for most things. You can load that thing with 2500 pounds in bed the way it's set up and got that number from Ford company themselves. But with the emission killed 400 it strains a bit with a reasonable load uphill and with a loaded cab over camper it is a pain in the you know what. With this swap I'm hoping to take care of some of that. Don't really haul a campest anymore but you never know. Thanks for the info and help again guys will post with updates.